1. Field of the Invention
The present invention relates to a modified epoxy resin having an excellent flexibility and containing a primary hydroxyl group excellent in the reactivity with a crosslinking agent, which is obtained by ring-opening polymerization of .epsilon.-caprolactone with the secondary hydroxyl group of an epoxy resin.
The present invention relates to a curable epoxy resin composition which comprises an epoxy resin internally plasticized with caprolactone, a polycarboxylic acid anhydride, and a curing promoter, and which cures to form highly flexible articles.
The present invention relates to a curable epoxy resin composition which comprises an epoxy resin internally plasticized with caprolactone and a polyamine, and which cures to form highly flexible articles.
The present invention relates a process for preparing a novel coating polyol resin excellent in flexibility reactivity with a crosslinking agent and the property of providing a coating having a high corrosion resistance by subjecting to ring-opening polymerization of secondary hydroxyl groups of a hydroxyl group-containing epoxy resin with .epsilon.-caprolactone and modifying the epoxy groups of the epoxy resin with an amine.
2. Description of Prior Arts
The class of epoxy resins, especially a glycidyl ether type epoxy resin prepared from bisphenol A and epichlorohydrin, includes a great variety of kinds ranging from a liquid resin to a solid resin having a high molecular weight, and this class of resins is widely used in various fields.
A liquid resin having a low molecular weight has a high reactivity in the epoxy group, and by utilizing this property, the resin is cured at normal temperatures with a polyamine or polyamide resin and used as an adhesive, FRP or a flooring material. Moreover, the liquid epoxy resin is heated and cured with a polybasic acid anhydride for the manufacture of cast products especially in the electric industry. On the other hand, a product having a high molecular weight is a brittle solid resin having a melting point of 60.degree. to 150.degree. C., and since this resin contains not only terminal epoxy groups but also secondary hydroxyl groups, it is widely used in the field of coating by utilizing the reactivity of these hydroxyl groups. For example, an epoxy ester obtained by esterification of this solid resin with an unsaturated fatty acid is used as an air-drying or normal temperature-drying paint. Furthermore, this epoxy resin is used as a baking paint including a melamine resin as a crosslinking agent or as a can-coating paint while being combined with a phenolic resin.
Moreover, this solid epoxy resin is powdered and mixed with a blocked isocyanate and is used as an epoxy type powder paint, or it is used for the cationic electrostatic coating.
Although the solid epoxy resin is used in various fields, since the resin is hard and brittle and the hydroxyl group is a secondary hydroxyl group, the reactivity with a crosslinking agent to be reacted with the hydroxyl group is poor and a high temperature is required for baking and crosslinking. Moreover, this epoxy resin is defective in that the weatherability is poor.
We made researches with a view to eliminating these defects of an epoxy resin and further broadening the possibility of using the epoxy resin, and we found that an appropriate flexibility is given to a hard and brittle epoxy resin by ring-opening polymerization of .epsilon.-caprolactone with the secondary hydroxyl group of the epoxy resin and simultaneously, the secondary hydroxyl group which is poor in the reactivity is converted to a primary hydroxyl group of the polycaprolactone having a high reactivity, and that in this modified epoxy resin, since the primary hydroxyl group is present at a point separate from the rigid epoxy resin skeleton, the reaction with a crosslinking agent is accelerated. We have now completed the present invention based on these findings.
It is well known to heat-cure an epoxy resin incorporated with a polycarboxylic acid anhydride with a curing promoter such as amines. The cured articles are, in general, superior in chemical, mechanical, and thermal properties, and find use as electrical parts and other articles in many industrial fields. They, however, are very hard, lacking flexibility, and are greatly strained by cure shrinkage. Many attempts have been made to overcome the disadvantage of the lack of flexibility. For example, it has been attempted to incorporate epoxy resins with a flexibilizer such as polybutadiene oligomers having carboxyl groups at both terminals, polyester resins having carboxyl groups, polyether resins having hydroxyl groups, polyester resins, and polyamide resins, or with a flexible epoxy resin like glycidyl ether which is prepared from polyether polyol and epichlorohydrin.
The above-mentioned attempts, however, are not necessarily successful because the resulting epoxy resins are poor in heat resistance, chemical resistance, and mechanical strength.
In order to develop a curable epoxy resin composition which is superior in flexibility, the present inventors carried out a series of studies which led to the findings that this object can be achieved by heat-curing caprolactone-modified epoxy resin and polycarboxylic acid anhydride with a curing promoter. The present invention is based on these findings.
It is well known to cure at room temperature or heat-cure an epoxy resin incorporated with a polyamine. The cured articles are, in general, superior in chemical, mechanical, and thermal properties, and find use as electrical parts, adhesives, and other articles in many industrial fields. They, however, are very hard, lacking flexibility, and are greatly strained by cure shrinkage. Many attempts have been made to impart flexibility. For example, it has been attempted to incorporate epoxy resins with a flexibilizer such as polybutadiene oligomers having carboxyl groups or hydroxyl groups at both terminals, polyester resins having carboxyl groups, polyether resins having hydroxyl groups, and polyester resins, or with a flexible epoxy resin like glycidyl ether which is prepared from polyether polyol and epichlorohydrin.
The above-mentioned attempts, however, are not necessarily successful because the resulting epoxy resins are poor in heat resistance, chemical resistance, and mechanical strength.
In order to develop a curable epoxy resin composition which is superior in flexibility, the present inventors carried out a series of studies which led to the findings that this object can be achieved by curing at room temperature or heat curing a caprolactone-modified epoxy resin with a polyamine. The present invention is based on these findings.
The class of epoxy resins, especially a glycidyl ether type epoxy resin prepared from bisphenol A and epichlorohydrin, includes a great variety of kinds ranging from a liquid resin to a solid resin having a high molecular weight, and this class of resins is widely used in various fields.
A liquid resin having a low molecular weight has a high reactivity in the epoxy group, and by utilizing this property, the resin is cured at normal temperatures with a polyamine or polyamide resin and used as an adhesive, FRP, a flooring material or an anti-corrosive paint. Moreover, the liquid epoxy resin is heated and cured with a polybasic acid anhydride for the manufacture of cast products especially in the electric industry. On the other hand, a product having a high molecular weight is a brittle solid resin having a melting point of 60.degree. to 150.degree. C., and it is widely used as a powdery casting resin in the electric industry by reacting it with an epoxy curing agent such as a polyamine, dicyane diamide, an imidazole or an acid anhydride. Furthermore, it is widely used in the field of coating by utilizing the reactivity of hydroxyl groups. For example, the solid epoxy resin is added to a melamine alkyd type baking paint so as to improve the corrosion resistance and adhesion. Moreover, an epoxy ester obtained by esterification of this solid resin with a fatty acid is used as a normal temperature-drying paint. Furthermore, this epoxy resin is used as a baking paint including a melamine resin as a crosslinking agent or as a can-coating paint while being combined with a phenolic resin.
Moreover, this solid epoxy resin is powdered and mixed with a blocked isocyanate and is used as an epoxy type powder paint, or it is used for the cationic electrostatic coating after the epoxy groups have been aminated and rendered water-soluble.
Although the solid epoxy resin is used in various fields, since the resin is hard and brittle and the hydroxyl group is a secondary hydroxyl group, the reactivity with a crosslinking agent to be reacted with the hydroxyl group is poor and a high temperature is required for baking and crosslinking. Moreover, this epoxy resin is defective in that the weatherability is poor or yellowing or chalking is caused.
We made researches with a view to eliminating these defects of an epoxy resin and further broadening the possibility of using the epoxy resin, and we found that an appropriate flexibility is given to a hard and brittle epoxy resin by ring-opening polymerizing of .epsilon.-caprolactone onto the secondary hydroxyl group of the epoxy resin and further modifying both terminal epoxy groups of the epoxy resin with an amine having an active hydrogen atom. In this way, the secondary hydroxyl group which is poor in the reactivity is converted to a primary hydroxyl group of the polycaprolactone having a high reactivity. In this modified epoxy resin, since the primary hydroxyl group is present at a point separate from the rigid epoxy resin skeleton, the reaction with a crosslinking agent is accelerated. Furthermore, it was found that since the epoxy resin is modified with an amine, the adhesion to a coated article and the corrosion resistance are highly improved. We have now completed the present invention based on these findings.